1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?2. Give an example of a double displacement reaction other than the one given in Activity 1.10.3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
\[
\begin{array}{l}
\text { (i) } 4 \mathrm{Na}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{Na}_{2} \mathrm{O}(\mathrm{s}) \
\text { (ii) } \mathrm{CuO}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})
\end{array}
\]
1. When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes.
The reaction involved is given below:
$Fe (s) + CuSO_4 (aq) → FeSO_4 (aq) + Cu (s)$
2. An example of a double displacement reaction is given below:
$ 2KBr (aq) + BaI_2 (aq) → 2KI (aq) + BaBr_2 (aq)$
3. (a) $4Na (s) + O_2 (g) → 2Na_2O (s)$ : In the given equation, Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.
(b) $CuO (s) + H_2 (g) → Cu (s) + H_2O (l)$ : In the given equation, Copper oxide (CuO) is reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H2O).
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